1. Field of the Invention
The present invention broadly relates to a laser clock and, more particularly, is concerned with a servo control system that improves the long-term stability of the clock by controlling errors due to optical dispersion effects caused by aging of the laser and change in its temperature.
2. Description of the Prior Art
The Air Force has requirements for both high accuracy timing sources and precision inertial navigation systems for advanced fighter aircraft. A laser clock proposed recently to meet these requirements is disclosed in the above cross referenced patent application. The laser clock utilizes a ring laser gyro which is also to be used in future aircraft for rotation rate sensing. Specifically, the laser clock includes a four frequency operating ring laser gyro with a Faraday rotator, such as described in U.S. Pat. No. 4,110,045 to Smith et al. Detector and electronic circuitry of the clock associated with the laser detects a beat frequency and converts it to a clock signal.
Frequency drift has been a problem associated with the laser clock. One cause of the problem is the temperature sensitivity of the Faraday rotator which includes frequency drift, which problem has been substantially overcome by second generation laser clock electronics. However, long term frequency drift due to optical dispersion effects caused by aging of the laser and temperature fluctuation thereof still remains to be resolved. Consequently, a need exists for a technique to satisfactorily control optical dispersion in the laser clock.